1. Field of the Invention
The present invention relates to a cooling device comprising a cooling fan and radiation fins and having a function of detecting that the radiation fins have clogged.
2. Description of the Related Art
There are conventionally known cooling devices having a plurality of radiation fins which are sequentially arranged at predetermined distances on a heat generating body wherein an air flow which flows in spaces between the adjacent radiation fins is generated by a cooling fan to cool the heat generating body. Among such conventional cooling devices, some are provided with a clogging detection function wherein the temperature of the heat generating body is monitored by a temperature sensor and when the temperature of the heat generating body exceeds a predetermined value, it is judged that the radiation fins have clogged.
A cooling device provided with such a clogging detection function is disclosed in Japanese Patent Application Laid-open No. 2014-165421 or Japanese Patent Application Laid-open No. 2014-098523, etc.
FIG. 4 schematically illustrates a conventional cooling device (which will be hereinafter referred to as the “cooling device of Prior Art 1”) disclosed in Japanese Patent Application Laid-open No. 2014-165421.
As can be seen in FIG. 4, in the cooling device of Prior Art 1, a dust-proof filter 101, a heat generating body 102, and a cooling fan 103 are sequentially arranged along the flow direction “A” of the air flow generated by the cooling fan 103. A first temperature sensor 104 is arranged on the upstream side of the dust-proof filter 101 in terms of the air flow direction “A”, and a second temperature sensor 105 is arranged on the downstream side of the dust-proof filter 101 in terms of the air flow direction “A”.
FIGS. 5A to 5C are diagrams showing changes over time of the temperatures detected by the first and second temperature sensors 104 and 105. In each of FIGS. 5A to 5C, the curved line indicated by B represents a temperature change over time, detected by the first temperature sensor 104 and the curved line indicated by C represents a temperature change over time, detected by the second temperature sensor 105. In particular, FIG. 5A shows temperature changes over time, detected by the first and second temperature sensors 104 and 105 when no clogging of the dust-proof filter 101 occurs and FIG. 5B shows temperature changes over time, detected by the first and second temperature sensors 104 and 105 when the dust-proof filter 101 has clogged.
When no clogging of the dust-proof filter 101 occurs, as can be seen in FIG. 5A, the temperatures detected by the first and second temperature sensors 104 and 105 do not exceed a predetermined temperature threshold S. However, once the dust-proof filter 101 clogs, as can be seen in FIG. 5B, the temperature detected by the second temperature sensor 105 exceeds the predetermined temperature threshold S. Thus, the cooling device of Prior Art 1 is adapted to judge that the dust-proof filter 101 has clogged when the detected temperature of the second temperature sensor 105 exceeds the temperature threshold S.
FIG. 6 schematically shows a conventional cooling device (which will be referred hereinafter as to the “cooling device of Prior Art 2”) disclosed in Japanese Patent Application Laid-open No. 2014-098523. The components corresponding to those of the cooling device of Prior Art 1 mentioned above are assigned the same reference numerals.
As shown in FIG. 6, in the cooling device of Prior Art 2, a dust-proof filter 101, a heat generating body 102 and a cooling fan 103 are sequentially arranged in the flow direction “A” of the air flow generated by the cooling fan 103. As can be seen in FIG. 6, a temperature sensor 106 is arranged in the vicinity of the heat generating body 102 to detect the ambient temperature of the heat generating body 102.
Furthermore, the cooling device of Prior Art 2 is provided with a temperature detection unit 107, a fan revolution control unit 108 for controlling the number of revolutions of the fan, and a clogging judgment unit 109, as can be seen in FIG. 6.
The temperature detection unit 107 monitors a temporary change of the temperature detected by the temperature sensor 106. The fan revolution control unit 108 increases and monitors the number of revolutions of the cooling fan 103 in accordance with the ambient temperature of the heat generating body 102 detected by the temperature sensor 106. The clogging judgment unit 109 is adapted to judge that the dust-proof filter 101 has clogged when the monitored number of revolutions of the cooling fan 103 exceeds a predetermined value.
However, in the aforementioned cooling device of Prior Art 1, even if no clogging of the dust-proof filter 101 occurs, when the heat generating body 102 generates heat due to an increase of the load thereof, the detection temperature of the second temperature sensor 105 may exceed the predetermined temperature threshold S as can be seen in FIG. 5C. In this case, it is erroneously judged that the dust-proof filter 101 has clogged. Consequently, the aforementioned cooling device of Prior Art 1 has a problem that clogging of the dust-proof filter 101 cannot be correctly detected.
The same problem may arise in the cooling device of Prior Art 2. Namely, in the cooling device of Prior Art 2 mentioned above, even if no clogging of the dust-proof filter 101 occurs, when the heat generating body 102 generates heat due to an increase of the load thereof, the number of revolutions of the cooling fan 103 may exceed a reference value in accordance with the ambient temperature of the heat generating body 102. In this case, it is erroneously judged that the dust-proof filter 101 has clogged. Consequently, the aforementioned cooling device of Prior Art 2 also has a problem that clogging of the dust-proof filter 101 cannot be correctly detected.
Moreover, a temperature change per unit time decreases as the thermal time constant of the cooling device increases in accordance with the coolability. Therefore, in the cooling device of Prior Art 1 and the cooling device of Prior Art 2 mentioned above, it may be impossible to correctly detect that the filter 101 has clogged without monitoring the temperature of the heat generating body 102 for a long time period.